The field of the invention relates to routing and alignment of beams in an optical system and more particularly to systems and methods for wave division multiplexing and/or demultiplexing for a fiber optic network.
Precision alignment of an optical beam through optical devices and systems may pose a variety of challenges. Devices may contain multiple optical elements, each having an associated alignment error that must be corrected. For instance, in optical multiplexing, a number of beams from different sources may need to be aligned with the tip of an optical fiber and each beam path may have different alignment error due to inaccuracies inherent in the fabrication and placement of optical components used in the device. One approach to alignment involves individually aligning the beam source and target, as well as each optical component, in multiple dimensions they are placed. Manipulating multiple interdependent components may be complex and time consuming, and may be difficult due to the size and configuration of the system. In addition, aligning the source or target can be difficult, since it may be electrically powered and have unique mounting or monitoring requirements. Also, the source or target may be the largest element and allowing for movement during alignment may increase the form factor of the entire device.
One example of an optical system requiring alignment is an optical network carrying multiple channels of information on an optical fiber. The information on each channel may be carried in an optical signal within a defined range of wavelengths that can be separated from the other channels. Wavelength division multiplexing (WDM) may be used to add a channel to the fiber or to combine and add a number of channels to the fiber. Wavelength division demultiplexing (WDDM) may be used to separate channels from the fiber.
One approach for WDDM is to use dispersion to separate the channels in an optical signal. However, it may be difficult to align the multiple dispersed channels with target fibers or other optical components intended to receive the separate channels. Among other things, temperature changes may cause thermal expansion or contraction of components that result in alignment error. Moreover, a long beam path may be required to achieve sufficient physical separation of the channels, which exacerbates alignment errors and may place limitations on the minimum size for the system.
Another approach involves using wavelength filters to separate individual channels from the incoming signal. In order to provide alignment, the signals may be carried to and from the filters by optical fibers coupled to the filters. However, a series of fiber loops may be required to route the signals to and from the filters, which can place limitations on the minimum size of the system. For instance, a WDDM may interface with a plurality of receive optical assemblies (ROSAs) which use a standard form factor, such as a GigaBaud Interface Converter (GBIC) form factor.
The GBIC specification was developed by a group of electronic manufacturers in order to arrive at a standard form factor transceiver module for use with a wide variety of serial transmission media and connectors. The specification defines the electronic, electrical, and physical interface of a removable serial transceiver module designed to operate at Gigabaud speeds. A GBIC provides a pluggable communication module which may be inserted and removed from a host or switch chassis without powering off the receiving socket. The GBIC form factor defines a module housing which includes a first electrical connector for connecting the module to a host device or chassis. This first electrical connector mates with a standard socket, which provides the interface between the host device printed circuit board and the module. The GBIC module itself is designed to slide into a mounting slot formed within the chassis of a host device.
Each GBIC may be coupled to an optical fiber loop that feeds into a filter. The fiber loops and other components may be included in a housing with a form factor much larger than the GBIC. Accordingly, one possible design for a 4-to-1 WDDM system would use four GBICs (one for receiving each channel) and a separate housing for the WDDM. In many applications, however, it may be desirable to provide a much more compact design, such as a WDM or WDDM that can be configured to fit within a single GBIC or smaller form factor.
Accordingly, there exists a need for improved methods and systems for routing and aligning beams and optical elements in an optical device, such as a WDM, WDDM or other optical device.
Improved methods and systems for routing and aligning beams and optical elements in an optical device, such as a WDM, WDDM or other optical device, are provided in accordance with embodiments of the present invention.
One aspect of the present invention provides an optical alignment element (OAE) that can be configured to substantially compensate for the cumulative alignment errors in the beam path. The OAE allows the optical elements in a device, other than the OAE, to be placed and fixed in place without substantially compensating for optical alignment errors. The OAE is inserted into the beam path and adjusted. This greatly increases the ease in the manufacturing of optical devices, especially for devices with numerous optical elements, and lowers the cost of manufacturing.
Another aspect of the present invention provides a compact multiplexer and/or demultiplex configuration which allows for the alignment of multiple folded beam paths to combine or separate optical channels. In one embodiment, a number of filters and mirrors are mounted on a core to route the beams. This aspect of the invention can be used to provide a very compact design and to permit flexibility in the placement of optical components. For instance, active components (such as lasers or optical receivers) may be positioned so that the electrical leads pass through the bottom of the device for convenient mounting to a printed circuit board, while an optical fiber which transmits or receives the optical signal from the network passes through the side of the device. The flexibility in routing, folding and aligning optical beams allows the components to be positioned conveniently for interfacing to external devices rather than being constrained by the alignment requirements of the device.
Another aspect of the present invention uses a compact form factor for a multiplexing device and/or demultiplexing device. The form factor may be a standard form factor typically used for a pluggable communications module which interfaces between serial transmission media and a host socket. These form factors may be defined for hot pluggable devices, such as receive optical sub-assemblies (ROSAs) and transmit optical sub-assemblies (TOSAs) in optical systems. Examples of these form factors include the GBIC form factor, the small form factor (SFF) and the small form pluggable (SFP) form factor. Aspects of the present invention provide for a compact multiplexer and/or demultiplexer using one of these form factors or an external housing and socket that is compatible with one of these form factors. This aspect of the invention can be used to provide a compact multiplexer and/or demultiplexer that can be inserted or removed from host sockets as part of a single module compatible with current host sockets used for ROSAs and TOSAs and thereby provide substantially more functionality with the same convenience.
In an exemplary embodiment, a multiplexing device is provided, which comprises: a plurality of components, wherein each component provides a beam with a channel in a range of wavelengths; a filter associated with each channel, wherein each filter is configured to select the beam for the respective channel; an output to receive the beam for each component after the beam traverses the respective filter; and an optical alignment element (OAE) associated with each channel, wherein the OAE can be configured to provide at least two directional changes in the path of the beam. In addition, in some embodiments, the path of the beam input to the OAE may be non-coplanar with the path of the beam output from the OAE.
In another exemplary embodiment, a demultiplexing device is provided, which comprises: an input, wherein the input provides a beam with a plurality of channels, each channel in a range of wavelengths; a filter associated with each channel, wherein each filter is configured to select the beam for the respective channel; a plurality of outputs associated with each channel, wherein each output receives the beam for the respective channel after the beam traverses the respective filter; and an OAE associated with each channel, wherein the OAE can be configured to provide at least two directional changes in the path of the beam. In addition, in some embodiments, the path of the beam input to the OAE may be non-coplanar with the path of the beam output from the OAE.
In another exemplary embodiment, a method for multiplexing a plurality of beams, each beam including a channel in a range of wavelengths is provided, which comprises the steps of: (a) traversing the plurality of beams through a plurality of filters, each filter associated with one of the channels, wherein each filter is configured to select the beam for the respective channel; (b) redirecting a path of each filtered beam using an OAE, wherein the OAE can be configured to provide at least two directional changes in the path of the filtered beam; and (c) outputting each filtered and redirected beam to a receiver. In addition, in some embodiments, the path of the beam input to the OAE may be non-coplanar with the path of the beam output from the OAE.
In another exemplary embodiment, a method for demultiplexing an optical signal, the optical signal including a plurality of channels in a range of wavelengths, is provided, which comprises the steps of: (a) traversing the optical signal through a plurality of filters, each filter associated with each channel, wherein each filter is configured to select the beam for the respective channel; (b) transmitting each channel after the beam traverses the respective filter; and (c) redirecting a path of each transmitted beam using an OAE, wherein the OAE can be configured to provide at least two directional changes in the path of the transmitted beam. In addition, in some embodiments, the path of the beam input to the OAE may be non-coplanar with the path of the beam output from the OAE.
In another exemplary embodiment, a frame is provided for assembling and aligning a multiplexer and/or demultiplexer. The frame forms a first plurality of openings and/or mounting surfaces, each configured to receive a light source or output element associated with a channel in a multiplexer or demultiplexer. The light source or output element may be fixed in place using hot wicking, solder, a press fit or interference fit or other method. The frame forms a second plurality of openings and/or mounting surfaces, each configured to receive a filter module associated with one of the channels to select the beam in the range of wavelengths for the respective channel. The filters may be fixed in place using hot wicking, solder, a press fit or interference fit or other method. The frame forms a third plurality of openings, each configured to receive an optical element associated with each channel in a position transverse to the beam for the respective channel. The opening for each optical element may be sized to allow the optical element to be moved within such opening for alignment prior to being fixedly mounted to the frame. The frame may be provided in exemplary embodiments by a core that fits into a chassis or by a unitary frame with holes and angled surfaces for inserting and/or mounting the optical components. In some embodiments additional optical components, such as mirrors or lenses, may be mounted to the frame.
Exemplary embodiments of the present invention may use one or more of the aspects described above, alone, or in combination.